Analysis of demicellization data from isothermal titration calorimetry

MICROCALORIMETRY Introduction Many industrial and biochemical applications depend on the usage of detergents and other surfactants. These compounds are indispensable, in particular, for the extraction, purification, and handling of membrane proteins. Owing to their amphiphilic nature, detergents can provide a membrane-mimetic environment required by integral membrane proteins to retain their native structures and functions in aqueous solution. Oftentimes, different detergents have to be screened to identify one that is suitable for the solubilization, stabilization, reconstitution, and biophysical, biochemical, or structural scrutiny of the protein of interest [1]. In each case, the membrane protein of interest dictates the suitability of a detergent, the choice of which depends on physicochemical properties such as chain length, headgroup size, and headgroup charge or polarity. However, a detergent found to be optimal for the isolation of a membrane protein need not necessarily be the best choice for downstream purification and in vitro studies. Harsh detergents such as SDS might inactivate the protein; some detergents such as Triton-X 100 absorb in the UV range and thus interfere with spectroscopic analysis; ionic detergents are unsuitable for isoelectric focusing or ion-exchange chromatography; and some detergents pose difficulties during membrane-protein reconstitution, that is, the reincorporation of the solubilized membrane protein into a lipid bilayer. Dialysis is a popular method for detergent removal to accomplish reconstitution, but long dialysis durations are required to remove detergents that have a low critical micellar concentration (CMC).